Substrate with a photocatalytic coating

ABSTRACT

The subject of the invention is a glass-, ceramic- or vitroceramic-based substrate ( 1 ) provided on at least part of at least one of its faces with a coating ( 3 ) with a photocatalytic property containing at least partially crystalline titanium oxide.  
     It also relates to the applications of such a substrate and to its method of preparation.

[0001] The invention relates to glass-, ceramic- or vitroceramic-basedsubstrates, more particularly made of glass, in particular transparentsubstrates, which are furnished with coatings with photocatalyticproperties, for the purpose of manufacturing glazing for variousapplications, such as utilitarian glazing or glazing for vehicles or forbuildings.

[0002] There is an increasing search to functionalize glazing bydepositing at the surface thereof thin layers intended to confer thereona specific property according to the targeted application. Thus, thereexist layers with an optical function, such as so-called anti-glarelayers composed of a stack of layers alternatively with high or lowrefractive indices. For an anti-static function or a heating function ofthe anti-icer type, it is also possible to provide electricallyconducting thin layers, for example based on metal or doped metal oxide.For an anti-solar or low-emissivity thermal function for example, thinlayers made of metal of the silver type or based on metal oxide ornitride may be used. To obtain a “rain-repellent” effect, it is possibleto provide layers with a hydrophobic nature, for example based onfluorinated organosilane and the like.

[0003] However, there still exists a need for a substrate, particularlya glazing, which could be described as “dirt-repellent”, that is to saytargeted at the permanence over time of the appearance and surfaceproperties, and which makes it possible in particular to render cleaningless frequent and/or to improve the visibility, by succeeding inremoving, as they are formed, the dirty marks which are graduallydeposited at the surface of a substrate, in particular dirty marks oforganic origin, such as finger marks or volatile organic productspresent in the atmosphere, or even dirty marks of condensation type.

[0004] In point of fact, it is known that there exist certainsemiconductive materials based on metal oxides which are capable, underthe effect of radiation of appropriate wavelength, of initiating radicalreactions which cause the oxidation of organic products; they aregenerally referred to as “photocatalytic” or alternatively“photoreactive” materials.

[0005] The aim of the invention is then to develop photocatalyticcoatings on a substrate which exhibit a marked “dirt-repellent” effectwith respect to the substrate and which can be manufacturedindustrially.

[0006] The object of the invention is a glass-, ceramic- orvitroceramic-based substrate, in particular made of glass andtransparent, provided on at least part of at least one of its faces witha coating with a photocatalytic property containing at least partiallycrystalline titanium oxide. The titanium oxide is preferablycrystallized “in situ” during the formation of the coating on thesubstrate.

[0007] Titanium oxide is in fact one of the semi-conductors which, underthe effect of light in the visible or ultraviolet range, degrade organicproducts which are deposited at their surface. The choice of titaniumoxide to manufacture a glazing with a “dirt-repellent” effect is thusparticularly indicated, all the more so since this oxide exhibits goodmechanical strength and good chemical resistance: for long-termeffectiveness, it is obviously important for the coating to retain itsintegrity, even if it is directly exposed to numerous attacks, inparticular during the fitting of the glazing on a building site(building) or on a production line (vehicle) which involves repeatedhandlings by mechanical or pneumatic prehension means, and also once theglazing is in place, with risks of abrasion (windscreen wipers, abrasiverag) and of contact with aggressive chemicals (atmospheric pollutants ofSO₂ type, cleaning product, and the like).

[0008] The choice has fallen, in addition, on a titanium oxide which isat least partially crystalline because it has been shown that it had amuch better performance in terms of photocatalytic property thanamorphous titanium oxide. It is preferably crystallized in the anataseform, in the rutile form or in the form of a mixture of anatase andrutile, with a degree of crystallization of at least 25%, in particularof approximately 30 to 80%, in particular close to the surface (theproperty being rather a surface property). (Degree of crystallization isunderstood to mean the amount by weight of crystalline TiO₂ with respectto the total amount by weight of TiO₂ in the coating).

[0009] It has also been possible to observe, in particular in the caseof crystallization in anatase form, that the orientation of the TiO₂crystals growing on the substrate had an effect on the photocatalyticbehaviour of the oxide: there exists a favoured orientation (1, 1, 0)which markedly promotes photocatalysis.

[0010] The coating is advantageously manufactured so that thecrystalline titanium oxide which it contains is in the form of“crystallites”, at least close to the surface, that is to say ofmonocrystals, having an average size of between 0.5 and 100 nm,preferably 1 to 50 nm, in particular 10 to 40 nm, more particularlybetween 20 and 30 nm. It is in fact in this size range that titaniumoxide appears to have an optimum photocatalytic effect, probably becausethe crystallites of this size develop a high active surface area.

[0011] As will be seen in more detail subsequently, it is possible toobtain the coating based on titanium oxide in many of ways:

[0012] by decomposition of titanium precursors (pyrolysis techniques:liquid pyrolysis, powder pyrolysis, pyrolysis in the vapour phase, knownas CVD (Chemical Vapour Deposition), or techniques associated with thesol-gel: dipping, cell coating, and the like),

[0013] by a vacuum technique (reactive or non-reactive cathodicsputtering).

[0014] The coating can also contain, in addition to the crystallinetitanium oxide, at least one other type of inorganic material, inparticular in the form of an amorphous or partially crystalline oxide,for example a silicon oxide (or mixture of oxides), titanium oxide, tinoxide, zirconium oxide or aluminium oxide. This inorganic material canalso participate in the photocatalytic effect of the crystallinetitanium oxide, by itself exhibiting to a certain extent aphotocatalytic effect, even a weak effect compared with that ofcrystalline TiO₂, which is the case with tin oxide or amorphous titaniumoxide.

[0015] A layer of “mixed” oxide thus combining at least partiallycrystalline titanium oxide with at least one other oxide can beadvantageous from an optical viewpoint, very particularly if the otheroxide or oxides are chosen with a lower index than that of TiO₂: bylowering the “overall” refractive index of the coating, it is possibleto vary the light reflection of the substrate provided with the coating,in particular to lower this reflection. This is the case if, forexample, a layer made of TiO₂/Al₂O₃, a method for the preparation ofwhich is described in Patent EP-0,465,309, or made of TiO₂/SiO₂ ischosen. It is necessary, of course, for the coating to contain however aTiO₂ content which is sufficient to maintain a significantphotocatalytic activity. It is thus considered that it is preferable forthe coating to contain at least 40% by weight, in particular at least50% by weight, of TiO₂ with respect to the total weight of oxide(s) inthe coating.

[0016] It is also possible to choose to superimpose, with the coatingaccording to the invention, a grafted oleophobic and/or hydrophobiclayer which is stable or resistant to photocatalysis, for example basedon the fluorinated organosilane described in patents U.S. Pat. No.5,368,892 and U.S. Pat. No. 5,389,427 and on the perfluoroalkylsilanedescribed in Patent Application FR-94/08734 of 13 Jul. 1994, publishedunder the number FR-2,722,493 and corresponding to European PatentEP-0,692,463, in particular of formula:

[0017] CF₃—(CF₂)_(n)-(CH₂)_(m)-SiX₃

[0018] in which n is from 0 to 12, m is from 2 to 5 and X is ahydrolysable group.

[0019] To amplify the photocatalytic effect of the titanium oxide of thecoating according to the invention, it is possible first of all toincrease the absorption band of the coating, by incorporating otherparticles in the coating, in particular metal particles or particlesbased on cadmium, tin, tungsten, zinc, cerium or zirconium.

[0020] It is also possible to increase the number of charge carriers bydoping the crystal lattice of the titanium oxide by inserting therein atleast one of the following metal elements: niobium, tantalum, iron,bismuth, cobalt, nickel, copper, ruthenium, cerium or molybdenum.

[0021] This doping can also be carried out by surface doping only of thetitanium oxide or of the combined coating, surface doping carried out bycovering at least part of the coating with a layer of metal oxides orsalts, the metal being chosen from iron, copper, ruthenium, cerium,molybdenum, vanadium and bismuth.

[0022] Finally, the photocatalytic phenomenon can be accentuated byincreasing the yield and/or the kinetics of the photocatalyticreactions, by covering the titanium oxide, or at least part of thecoating which incorporates it, with a noble metal in the form of a thinlayer of the platinum, rhodium, silver or palladium type.

[0023] Such a catalyst, for example deposited by a vacuum technique, infact makes it possible to increase the number and/or the lifetime of theradical entities created by the titanium oxide and thus to promote thechain reactions leading to the degradation of organic products.

[0024] In an entirely surprising way, the coating exhibits in fact notone property but two, as soon as it is exposed to appropriate radiation,as in the visible and/or ultraviolet field, such as sunlight: by thepresence of photocatalytic titanium oxide, as already seen, it promotesthe gradual disappearance, as they are accumulated, of dirty marks oforganic origin, their degradation being caused by a radical oxidationprocess. Inorganic dirty marks are not, themselves, degraded by thisprocess: they therefore remain on the surface and, except for a degreeof crystallization, they are in part easily removed since they no longerhave any reason to adhere to the surface, the binding organic agentsbeing degraded by photocatalysis.

[0025] However, the coating of the invention, which is permanentlyself-cleaning, also preferably exhibits an external surface with apronounced hydrophilic and/or oleophilic nature which results in threevery advantageous effects:

[0026] a hydrophilic nature makes possible complete wetting of the waterwhich can be deposited on the coating. When a water condensationphenomenon takes place, instead of a deposit of water droplets in theform of condensation which hampers visibility, there is in fact acontinuous thin film of water which is formed on the surface of thecoating and which is entirely transparent. This “anti-condensation”effect is in particular demonstrated by the measurement of a contactangle with water of less than 5° after exposure to light, and

[0027] after running of water, in particular of rain, over a surfacewhich has not been treated with a photocatalytic layer, many drops ofrainwater remain stuck to the surface and leave, once evaporated,unattractive and troublesome marks, mainly of inorganic origin. Indeed,a surface exposed to the surrounding air is rapidly covered by a layerof dirty marks which limits the wetting thereof by water. These dirtymarks are in addition to the other dirty marks, in particular inorganicmarks (crystallizations and the like), contributed by the atmosphere inwhich the glazing bathes. In the case of a photoreactive surface, theseinorganic dirty marks are not directly degraded by photocatalysis. Infact, they are in very large part removed by virtue of the hydrophilicnature induced by the photocatalytic activity. This hydrophilic natureindeed causes complete spreading of the drops of rain. Evaporation marksare therefore no longer present. Moreover, the other inorganic dirtymarks present on the surface are washed, or redissolved in the case ofcrystallization, by the water film and are thus in large part removed.An “inorganic dirt-repellent” effect is obtained, induced in particularby rain,

[0028] in conjunction with a hydrophilic nature, the coating can alsoexhibit an oleophilic nature which makes possible the “wetting” of theorganic dirty marks which, as with water, then tend to be deposited onthe coating in the form of a continuous film which is less visible thanhighly localized “stains”. An “organic dirt-repellent” effect is thusobtained which operates in two ways: as soon as it is deposited on thecoating, the dirty mark is already not very visible. Subsequently, itgradually disappears by radical degradation initiated by photocatalysis.

[0029] The coating can be chosen with a more or less smooth surface. Adegree of roughness can indeed be advantageous:

[0030] it makes it possible to develop a greater active photocatalyticsurface area and thus induces a greater photocatalytic activity,

[0031] it has a direct effect on the wetting. The roughness in factenhances the wetting properties. A smooth hydophilic surface will beeven more hydrophilic once rendered rough. “Roughness” is understood tomean, in this instance, both the surface roughness and the roughnessinduced by a porosity of the layer in at least a portion of itsthickness.

[0032] The above effects will be all the more marked when the coating isporous and rough, resulting in a superhydrophilic effect for roughphotoreactive surfaces. However, when exaggerated, the roughness can bepenalizing by promoting incrustation or accumulation of dirty marksand/or by bringing about the appearance of an optically unacceptablelevel of fuzziness.

[0033] It has thus proved to be advantageous to adapt the method fordeposition of TiO₂-based coatings so that they exhibit a roughness ofapproximately 2 to 20 nm, preferably of 5 to 15 nm, this roughness beingevaluated by atomic force microscopy, by measurement of the value of theroot mean square or RMS over a surface area of 1 square micrometre. Withsuch roughnesses, the coatings exhibit a hydrophilic nature which isreflected by a contact angle with water which can be less than 1°. Ithas also been found that it is advantageous to promote a degree ofporosity in the thickness of the coating. Thus, if the coating consistsonly of TiO₂, it preferably exhibits a porosity of the order of 65 to99%, in particular of 70 to 90%, the porosity being defined in thisinstance indirectly by the percentage of the theoretical relativedensity of TiO₂, which is approximately 3.8. One means for promotingsuch a porosity comprises, for example, the deposition of the coating bya technique of the sol-gel type involving the decomposition of materialsof organometallic type: an organic polymer of polyethylene glycol PEGtype can then be introduced into the solution, in addition to theorganometallic precursor(s): on curing the layer by heating, the PEG isburnt off, which brings about or accentuates a degree of porosity in thethickness of the layer.

[0034] The thickness of the coating according to the invention isvariable; it is preferably between 5 nm and 1 micron, in particularbetween 5 and 100 nm, in particular between 10 and 80 nm, or between 20and 50 nm. In fact, the choice of the thickness can depend on variousparameters, in particular on the targeted application of the substrateof the glazing type or alternatively on the size of the TiO₂crystallites in the coating or on the presence of a high proportion ofalkali metals in the substrate.

[0035] It is possible to arrange, between the substrate and the coatingaccording to the invention, one or a number of other thin layers with adifferent or complementary function to that of the coating. It canconcern, in particular, layers with an anti-static, thermal or opticalfunction or promoting the crystalline growth of TiO₂ in the anatase orrutile form or of layers forming a barrier to the migration of certainelements originating from the substrate, in particular forming a barrierto alkali metals and very particularly to sodium ions when the substrateis made of glass.

[0036] It is also possible to envisage a stack of alternating“anti-glare” layers of thin layers with high and low indices, thecoating according to the invention constituting the final layer of thestack. In this case, it is preferable for the coating to have arelatively low refractive index, which is the case when it is composedof a mixed oxide of titanium and of silicon.

[0037] The layer with an anti-static and/or thermal function (heating byproviding it with power leads, low-emissive, anti-solar, and the like)can in particular be chosen based on a conductive material of the metaltype, such as silver, or of the doped metal oxide type, such as indiumoxide doped with tin ITO, tin oxide doped with a halogen of the fluorinetype SnO₂:F or with antimony SnO₂:Sb or zinc oxide doped with indiumZnO:In, with fluorine ZnO:F, with aluminium ZnO:Al or with tin ZnO:Sn.It can also concern metal oxides which are stoichiometrically deficientin oxygen, such as SnO_(2-x) or ZnO_(2-x) with x<2.

[0038] The layer with an anti-static function preferably has a surfaceresistance value of 20 to 1000 ohms.square. Provision can be made forfurnishing it with power leads in order to polarize it (feeding voltagesfor example of between 5 and 100 V). This controlled polarization makesit possible in particular to control the deposition of dust with a sizeof the order of a millimetre capable of being deposited on the coating,in particular dry dust which adheres only by an electrostatic effect: bysuddenly reversing the polarization of the layer, this dust is“ejected”.

[0039] The thin layer with an optical function can be chosen in order todecrease the light reflection and/or to render more neutral the colourin reflection of the substrate. In this case, it preferably exhibits arefractive index intermediate between that of the coating and that ofthe substrate and an appropriate optical thickness and can be composedof an oxide or of a mixture of oxides of the aluminium oxide Al₂O₃, tinoxide SnO₂, indium oxide In₂O₃ or silicon oxycarbide or oxynitride type.In order to obtain maximum attenuation of the colour in reflection, itis preferable for this thin layer to exhibit a refractive index close tothe square root of the product of the squares of the refractive indicesof the two materials which frame it, that is to say the substrate andthe coating according to the invention. In the same way, it isadvantageous to choose its optical thickness (that is to say the productof its geometric thickness and of its refractive index) similar tolambda/4, lambda being approximately the average wavelength in thevisible, in particular from approximately 500 to 550 nm.

[0040] The thin layer with a barrier function with respect to alkalimetals can be in particular chosen based on silicon oxide, nitride,oxynitride or oxycarbide, made of aluminium oxide containing fluorineAl₂O₃:F or alternatively made of aluminium nitride. In fact, it hasproved to be useful when the substrate is made of glass, because themigration of sodium ions into the coating according to the inventioncan, under certain conditions, detrimentally affect the photocatalyticproperties thereof.

[0041] The nature of the substrate or of the sublayer furthermore has anadditional advantage: it can promote the crystallization of thephotocatalytic layer which is deposited, in particular in the case ofCVD deposition.

[0042] Thus, during deposition of TiO₂ by CVD, a crystalline SnO₂:Fsublayer promotes the growth of TiO₂ mostly in the rutile form, inparticular for deposition temperatures of the order of 400° to 500° C.,whereas the surface of a soda-lime glass or of a silicon oxycarbidesublayer rather induces an anatase growth, in particular for depositiontemperatures of the order of 400° to 600° C.

[0043] All these optional thin layers can, in a known way, be depositedby vacuum techniques of the cathodic sputtering type or by othertechniques of the thermal decomposition type, such as solid, liquid orgas phase pyrolyses. Each of the abovementioned layers can combine anumber of functions but it is also possible to superimpose them.

[0044] Another subject of the invention is “dirt-repellent” (organicand/or inorganic dirty marks) and/or “anti-condensation” glazing,whether it is monolithic or insulating multiple units of the doubleglazing or laminated type, which incorporates the coated substratesdescribed above.

[0045] The invention is thus targeted at the manufacture of glass,ceramic or vitroceramic products and very particularly at themanufacture of “self-cleaning” glazing. The latter can advantageously bebuilding glazing, such as double glazing (it is then possible to arrangethe coating “external side” and/or “internal side”, that is to say onface 1 and/or on face 4). This proves to be very particularlyadvantageous for glazing which is not very accessible to cleaning and/orwhich needs to be cleaned very frequently, such as roofing glazing,airport glazing, and the like. It can also relate to vehicle windowswhere maintenance of visibility is an essential safety criterion. Thiscoating can thus be deposited on car windscreens, side windows or rearwindows, in particular on the face of the windows turned towards theinside of the passenger compartment. This coating can then prevent theformation of condensation and/or remove traces of dirty finger mark,nicotine or organic material type, the organic material being of thevolatile plasticizing type released by the plastic lining the interiorof the passenger compartment, in particular that of the dashboard(release sometimes known under the term “fogging”). Other vehicles suchas planes or trains can also find it advantageous to use windowsfurnished with the coating of the invention.

[0046] A number of other applications are possible, in particular foraquarium glass, shop windows, greenhouses, verandas, or glass used ininterior furniture or street furniture but also mirrors, televisionscreens, the spectacle field or any architectural material of the facingmaterial, cladding material or roofing material type, such as tiles, andthe like.

[0047] The invention thus makes it possible to functionalize these knownproducts by conferring on them anti-ultraviolet, dirt-repellent,bactericidal, anti-glare, anti-static or antimicrobial properties andthe like.

[0048] Another advantageous application of the coating according to theinvention consists in combining it with an electrically controlledvariable absorption glazing of the following types: electrochromicglazing, liquid crystal glazing, optionally with dichroic dye, glazingcontaining a system of suspended particles, viologen glazing and thelike. As all these glazing types are generally composed of a pluralityof transparent substrates, between which are arranged the “active”elements, it is then possible advantageously to arrange the coating onthe external face of at least one of these substrates.

[0049] In particular in the case of an electrochromic glazing, when thelatter is in the coloured state, its absorption results in a degree ofsurface heating which, in fact, is capable of accelerating thephotocatalytic decomposition of the carbonaceous substances which aredeposited on the coating according to the invention. For further detailson the structure of an electrochromic glazing, reference willadvantageously be made to Patent Application EP-A-0,575,207, whichdescribes an electrochromic laminated double glazing, it being possiblefor the coating according to the invention preferably to be positionedon face 1.

[0050] Another subject of the invention is the various processes forobtaining the coating according to the invention. It is possible to usea deposition technique of the pyrolysis type which is advantageousbecause it in particular makes possible the continuous deposition of thecoating directly on the float-glass strip when a is glass substrate isused.

[0051] The pyrolysis can be carried out in the solid phase, frompowder(s) of precursor(s) of the organometallic type.

[0052] The pyrolysis can be carried out in the liquid phase, from asolution comprising an organometallic titanium precursor of the titaniumchelate and/or titanium alcoholate type. Such precursors are mixed withat least one other organometallic precursor. For further details on thenature of the titanium precursor or on the deposition conditions,reference will be made, for example, to Patents FR-2,310,977 andEP-0,465,309.

[0053] The pyrolysis can also be carried out in the vapour phase, whichtechnique is also denoted under the term of CVD (Chemical VapourDeposition), from at least one titanium precursor of the halide type,such as TiCl₄, or titanium alcoholate of the Ti tetraisopropylate type,Ti(OiPr)₄. The crystallization of the layer can additionally becontrolled by the type of sublayer, as mentioned above.

[0054] It is also possible to deposit the coating by other techniques,in particular by techniques in combination with the “sol-gel”. Variousdeposition methods are possible, such as “dipping”, also known as “dipcoating”, or a deposition using a cell known as “cell coating”. It canalso concern a method of deposition by “spray coating” or by laminarcoating, the latter technique being described in detail in PatentApplication WO-94/01598. All these deposition methods in general use asolution comprising at least one organometallic precursor, in particulartitanium of the alcoholate type, which is thermally decomposed aftercoating the substrate with the solution on one of its faces or on bothits faces.

[0055] It can be advantageous, moreover, to deposit the coating,whatever the deposition technique envisaged, not in a single step butvia at least two successive stages, which appears to promote thecrystallization of titanium oxide throughout the thickness of thecoating when a relatively thick coating is chosen.

[0056] Likewise, it is advantageous to subject the coating with aphotocatalytic property, after deposition, to a heat treatment of theannealing type. A heat treatment is essential for a technique of thesol-gel or laminar coating type in order to decompose the organometallicprecursor(s) to oxide, once the substrate has been coated, and toimprove the resistance to abrasion, which is not the case when apyrolysis technique is used, where the precursor decomposes as soon asit comes into contact with the substrate. In the first case, as in thesecond, however, a post-deposition heat treatment, once the TiO₂ hasbeen formed, improves its degree of crystallization. The chosentreatment temperature can in addition make possible better control ofthe degree of crystallization and of the crystalline nature, anataseand/or rutile, of the oxide.

[0057] However, in the case of a substrate made of soda-lime glass,multiple and prolonged annealings can promote attenuation of thephotocatalytic activity because of an excessive migration of the alkalimetals from the substrate towards the photoreactive layer. The use of abarrier layer between the substrate, if it is made of standard glass,and the coating, or the choice of a substrate made of glass with anappropriate composition, or alternatively the choice of a soda-limeglass with a surface from which alkali metals have been eliminated makeit possible to remove this risk.

[0058] Other advantageous details and characteristics of the inventionemerge from the description below of non-limiting implementationalexamples, with the help of the following figures:

[0059]FIG. 1: a cross-section of a glass substrate provided with thecoating according to the invention,

[0060]FIG. 2: a diagram of a sol-gel deposition technique, by so-called“dip coating” the coating,

[0061]FIG. 3: a diagram of a so-called “cell coating” depositiontechnique,

[0062]FIG. 4: a diagram of a so-called “spray coating” depositiontechnique,

[0063]FIG. 5: a diagram of a deposition technique by laminar coating.

[0064] As represented very diagrammatically in FIG. 1, all the followingexamples relate to the deposition of a so-called “dirt-repellent”coating 3, essentially based on titanium oxide, on a transparentsubstrate 1.

[0065] The substrate 1 is made of clear soda-lime-silica glass with athickness of 4 mm and a length and width of 50 cm. It is obvious thatthe invention is not limited to this specific type of glass. The glasscan in addition not be flat but bent.

[0066] Between the coating 3 and the substrate 1 is found a thinoptional layer 2, either based on silicon oxycarbide, written as SiOC,for the purpose of constituting a barrier to the diffusion of the alkalimetals and/or a layer which attenuates light reflection, or based on tinoxide doped with fluorine SnO₂:F, for the purpose of constituting ananti-static and/or low-emissive layer, even with a not very pronouncedlow-emissive effect, and/or a layer which attenuates the colour, inparticular in reflection.

EXAMPLES 1 TO 3

[0067] Examples 1 to 3 relate to a coating 3 deposited using a liquidphase pyrolysis technique. The operation can be carried outcontinuously, by using a suitable distribution nozzle arrangedtransversely and above the float-glass strip at the outlet of thefloat-bath chamber proper. In this instance, the operation is carriedout non-continuously, by using a moveable nozzle arranged opposite thesubstrate 1 already cut to the dimensions shown, which substrate isfirst heated in an oven to a temperature of 400 to 650° C. beforeprogressing a constant speed past the nozzle spraying at an appropriatesolution.

Example 1

[0068] In this example, there is no optional layer 2. The coating 3 isdeposited using a solution comprising two organometallic titaniumprecursors, titanium diisopropoxide diacetylacetonate and titaniumtetraoctyleneglycolate, dissolved in a mixture of two solvents, thelatter being ethyl acetate and isopropanol.

[0069] It should be noted that it is also entirely possible to use otherprecursors of the same type, in particular other titanium chelates ofthe titanium acetylacetonate, titanium (methyl acetoacetato), titanium(ethyl acetoacetato) or alternatively titanium triethanolaminato ortitanium diethanolaminato type.

[0070] As soon as the substrate 1 has reached the desired temperature inthe oven, i.e. in particular approximately 500° C., the substrateprogresses past the nozzle which sprays at room temperature, usingcompressed air, the mixture shown.

[0071] A TiO₂ layer with a thickness of approximately 90 nm is thenobtained, it being possible for the thickness to be controlled by therate of progression of the substrate 1 past the nozzle and/or thetemperature of the said substrate. The layer is partially crystalline inthe anatase form.

[0072] This layer exhibits excellent mechanical behaviour. Itsresistance to abrasion tests is comparable with that obtained for thesurface of the bare glass.

[0073] It can be bent and dip coated. It does not exhibit bloom: thescattered light transmission of the coated substrate is less than 0.6%(measured according to the D₆₅ illuminant at 560 nm)

Example 2

[0074] Example 1 is repeated but inserting, between the substrate 1 andcoating 3, an SnO₂:F layer 2 with a thickness of 73 nm. This layer isobtained by powder pyrolysis from dibutyltin difluoride DBTF. It canalso be obtained, in a known way, by pyrolysis in the liquid or vapourphase, as is for example described in Patent Application EP-A-0,648,196.In the vapour phase, it is possible in particular to use a mixture ofmonobutyltin trichloride and of a fluorinated precursor optionally incombination with a “mild” oxidant of the H₂O type.

[0075] The index of the layer obtained is approximately 1.9. Its surfaceresistance is approximately 50 ohms.

[0076] In the preceding Example 1, the coated substrate 1, mounted as adouble glazing so that the coating is on face 1 (with another substrate1′ which is non-coated but of the same nature and dimensions as thesubstrate 1 via a 12 mm layer of air), exerts a colour saturation valuein reflection of 26% and a colour saturation value in transmission of6.8%.

[0077] In this Example 2, the colour saturation in reflection (in thegoldens) is only 3.6% and it is 1.1% in transmission.

[0078] Thus, the SnO₂:F sublayer makes it possible to confer, on thesubstrate, anti-static properties due to its electrical conductivity andit also has a favourable effect on the colorimetry of the substrate, bymaking its coloration markedly more “neutral”, both in transmission andin reflection, which coloration is caused by the presence of thetitanium oxide coating 3 exhibiting a relatively high refractive index.It is possible to polarize it by providing it with a suitable electricalsupply, in order to limit the deposition of dust with a relatively largesize, of the order of a millimetre.

[0079] In addition, this sublayer decreases the diffusion of alkalimetals into the photocatalytic TiO₂ layer. The photocatalytic activityis thus improved.

Example 3

[0080] Example 2 is repeated but this time inserting, between substrate1 and coating 3, a layer 2 based on silicon oxycarbide with an index ofapproximately 1.75 and a thickness of approximately 50 nm, which layercan be obtained by CVD from a mixture of SiH₄ and ethylene diluted innitrogen, as described in Patent Application EP-A-0,518,755. This layeris particularly effective in preventing the tendency of alkali metals(Na⁺, K⁺) and of alkaline-earth metals (Ca⁺⁺) originating from thesubstrate 1 to diffuse towards the coating 3 and thus the photocatalyticactivity is markedly improved. As it has, like SnO₂:F, a refractiveindex intermediate between that of the substrate (1.52) and of thecoating 3 (approximately 2.30 to 2.35), it also makes it possible toreduce the intensity of the coloration of the substrate, both inreflection and in transmission, and overall to decrease the lightreflection value R_(L) of the said substrate.

[0081] The following Examples 4 to 7 relate to depositions by CVD.

EXAMPLES 4 TO 7 Example 4

[0082] This example relates to the deposition by CVD of the coating 3directly on the substrate 1 using a standard nozzle, such as thatrepresented in the above-mentioned Patent Application EP-A-0,518,755.Use is made, as precursors, either of an organometallic compound or of ametal halide. In this instance, titanium tetraisopropylate is chosen asorganometallic compound, this compound being advantageous because of itshigh volatility and its large working temperature range, from 300 to650° C. In this example, deposition is carried out at approximately 425°C. and the TiO₂ thickness is 15 nm.

[0083] Tetraethoxytitanium Ti(O-Et)₄ may also be suitable and, ashalide, mention may be made of TiCl₄.

Example 5

[0084] It is carried out similarly to Example 4, except that, in thisinstance, the 15 nm TiO₂ layer is not deposited directly on the glassbut on a 50 nm SiOC sublayer deposited as in Example 3.

Example 6

[0085] It is carried out as in Example 4, except that, in this instance,the thickness of the TiO₂ layer is 65 nm.

Example 7

[0086] It is carried out as in Example 5, except that, in this instance,the thickness of the TiO₂ layer is 60 nm.

[0087] From these Examples 4 to 7, it is found that the substrates thuscoated exhibit good mechanical behaviour with respect to the abrasiontests. In particular, no delamination of the TiO₂ layer is observed.

Example 8

[0088] This example uses a technique in combination with the sol-gelusing a deposition method by “dipping”, also known as “dip coating”, theprinciple of which emerges from FIG. 2: it consists in immersing thesubstrate 1 in the liquid solution 4 containing the appropriateprecursor(s) of the coating 3 and in then withdrawing the substrate 1therefrom at a controlled rate using a motor means 5, the choice of therate of withdrawal making it possible to adjust the thickness ofsolution remaining at the surface of the two faces of the substrate and,in fact, the thickness of the coatings deposited, after heat treatmentof the latter in order both to evaporate the solvent and to decomposethe precursor or precursors to oxide.

[0089] Use is made, for depositing the coating 3, of a solution 4comprising either titanium tetrabutoxide Ti(O-Bu)₄, stabilized withdiethanolamine DEA in the molar proportion 1:1, in an ethanol-typesolvent containing 0.2 mol of tetrabutoxide per litre of ethanol, or themixture of precursors and of solvents described in Example 1. (Anotherprecursor, such as titanium (diethanolaminato)dibutoxide, can also beused).

[0090] The substrates 1 can contain SiOC sublayers.

[0091] After withdrawal from each of the solutions 4, the substrates 1are heated for 1 hour at 100° C. and then for approximately 3 hours at550° C. with the temperature raised gradually.

[0092] A coating 3 is obtained on each of the faces, which coating is inboth cases made of highly crystalline TiO₂ in the anatase form.

Example 9

[0093] This example uses the technique known as “cell coating”, theprinciple of which is recalled in FIG. 3. It relates to forming a narrowcavity, delimited by two substantially parallel faces 6, 7 and two seals8, 9, at least one of these faces 6, 7 consisting of the face of thesubstrate 1 to be treated. The cavity is then filled with the solution 4of precursor(s) of the coating and the solution 4 is withdrawn in acontrolled way, so as to form a wetting meniscus, for example using aperistaltic pump 10, leaving a film of the solution 4 on the face of thesubstrate 1 as this solution is withdrawn.

[0094] The cavity 5 is then maintained for at least the time necessaryfor drying. The film is cured by heat treatment. The advantage of thistechnique, in comparison with “dip coating”, is in particular that it ispossible to treat only a single one of the two faces of the substrate 1and not both systematically, unless a masking system is resorted to.

[0095] The substrates 1 comprise thin layers 2 based on siliconoxycarbide SiOC.

[0096] Example 6 uses respectively the solutions 4 described in Example8. The same heat treatments are then carried out in order to obtain theTiO₂ coating 3.

[0097] The coating 3 exhibits good mechanical durability.

[0098] Under an SEM (scanning electron microscope), a field effectappears in the form of “grains” of monocrystals with a diameter ofapproximately 30 nm. The roughness of this coating induces wettingproperties which are enhanced with respect to a non-rough coating.

[0099] These same solutions 4 can also be used to deposit coatings by“spray coating”, as represented in FIG. 4, where the solution 4 issprayed in the form of a cloud against the substrate 1 statically, or bylaminar coating, as represented in FIG. 5. In the latter case, thesubstrate 1, held by vacuum suction against a support 11 made ofstainless steel and Teflon, is passed over a tank 12 containing thesolution, in which solution is partially immersed a slotted cylinder 14,and the combined tank 12 and cylinder 14 are then moved, over the wholelength of the substrate 1, the mask 13 preventing excessive evaporationof the solvent from the solution 4. For further details regarding thislatter technique, reference will advantageously be made to theabovementioned Patent Application WO-94/01598.

[0100] Tests were carried out on the substrates obtained according tothe above examples in order to characterize the coatings deposited andto evaluate their “anti-condensation” and “dirt-repellent” behaviour.

[0101] Test 1: This is the test of the condensation aspects. It consistsin observing the consequences of the photocatalysis and of the structureof the coating (level of hydroxyl groups, porosity, roughness) on thewetting. If the surface is photo-reactive, the carbonaceousmicrocontaminants which are deposited on the coating are continuallydestroyed and the surface is hydrophilic and thus anti-condensation. Itis also possible to carry out a quantitative evaluation by suddenlyreheating the initially coated substrate, stored in the cold or simplyby blowing over the substrate, by measuring if condensation appears and,in the affirmative, at what time, and by then measuring the timenecessary for the disappearance of the said condensation.

[0102] Test 2: It relates to the evaluation of the hydrophilicity andthe oleophilicity at the surface of the coating 3, in comparison withthose of the surface of a bare glass, by measurement of contact anglesof a drop of water and of a drop of DOP (dioctyl phthalate) at theirsurfaces, after having left the substrates for one week in thesurrounding atmosphere under natural light, in the dark and then havingsubjected them to UVA radiation for 20 minutes.

[0103] Test 3: It consists in depositing, on the substrate to beevaluated, a layer of an organosilane and in irradiating it with UVAradiation so as to degrade it by photocatalysis. As the organosilanemodifies the wetting properties, measurements of contact angle of thesubstrate with water during the irradiation indicate the state ofdegradation of the grafted layer. The rate of disappearance of thislayer is related to the photocatalytic activity of the substrate.

[0104] The grafted organosilane is a trichlorosilane:octadecyltrichlorosilane (OTS). The grafting is carried out by dipping.

[0105] The test device is composed of a turntable rotating around from 1to 6 low pressure UVA lamps. The test specimens to be evaluated areplaced in the turntable, the face to be evaluated on the side of the UVAradiation. Depending on their position and the number of lamps switchedon, each test specimen receives a UVA irradiation varying from 0.5 W/m²to 50 W/m². For Examples 1, 2, 3, 8 and 9, the irradiation power ischosen as 1.8 W/m² and, for Examples 4 to 7, as 0.6 W/m².

[0106] The time between each measurement of the contact angle variesbetween 20 min and 3 h, depending on the photocatalytic activity of thetest specimen under consideration. The measurements are carried outusing a goniometer.

[0107] Before irradiation, the glasses exhibit an angle of approximately100°. It is considered that the layer is destroyed after irradiationwhen the angle is less than 20°.

[0108] Each test specimen tested is characterized by the mean rate ofdisappearance of the layer, given in nanometres per hour, that is to saythe thickness of the organosilane layer deposited divided by theirradiation time which makes it possible to reach a final stationaryvalue of less than 20° (time for disappearance of the organosilanelayer).

[0109] All the preceding examples pass Test 1, that is to say that, whenthe substrates coated with the coating are blown on, they remainperfectly transparent, whereas a highly visible layer of condensation isdeposited on non-coated substrates.

[0110] The examples were subjected to Test 2: the coated substrates,after exposure to UVA radiation, exhibit a contact angle with water andwith DOP of not more than 5°. In contrast, a bare glass under the sameconditions exhibits a contact angle with water of 40° and a contactangle with DOP of 20°.

[0111] The results of the substrates coated according to the aboveexamples in Test 3 are combined in the table below. Test 3, of wetting,at 1.8 W/m² UVA Substrate (in nm/h) Example 1 (TiO₂ on bare glass) 0.03Example 2 (TiO₂ on SnO₂:F) 0.1 Example 3 (TiO₂ on SiOC) 0.2 Example 8(TiO₂ on 50 nm SiOC) 5 Example 9 (TiO₂ on 50 nm SiOC) 5 Bare glass 0Test 3, of wetting, at 0.6 W/m² UVA Substrate (CVD) (in nm/h) Example 4(TiO₂ on bare glass) <0.05 nm/h Example 5 (TiO₂ on SiOC) 4 Example 6(TiO₂ on bare glass) 9 Example 7 (TiO₂ on SiOC) 19.5

[0112] From the table, it can be seen that the presence of sublayers, inparticular of SiOC, promotes the photocatalytic activity of the coatingcontaining the TiO₂, by its barrier effect to alkali metals andalkaline-earth metals which can migrate from the glass (comparison ofExamples 4 and 5 or 6 and 7).

[0113] It is also observed that the thickness of the coating containingthe TiO₂ also plays a role (comparison of Examples 1 and 3): for a TiO₂coating with a thickness greater than the mean size of the monocrystalsor “crystallites”, a better photocatalytic effect is obtained.

[0114] Indeed, it could be observed that the TiO₂ coatings obtained byCVD exhibit the most advanced crystallization, with crystallite sizes ofthe order of 20 to 30 nm. It can be seen that the photocatalyticactivity of Example 6 (65 nm of TiO₂) is markedly greater than that ofExample 4 (15 nm of TiO₂ only). It is therefore advantageous to providea TiO₂ coating thickness at least two times greater than the meandiameter of the crystallites which it contains. Alternatively, as in thecase of Example 5, it is possible to retain a TiO₂ coating with a thinthickness but then to choose to use a sublayer of an appropriate natureand with an appropriate thickness for promoting as far as possible thecrystalline growth of TiO₂ from the “first” layer of crystallites.

[0115] It could be observed that the crystallization of the TiO₂ wassomewhat less advanced for the coatings deposited by a technique otherthan CVD. Here again, however, everything is still a matter ofcompromise: a less advanced crystallization and an a priori lowerphotocatalytic activity can be “compensated for” by the use of adeposition process which is less expensive or less complex, for example.Moreover, the use of an appropriate sublayer or the doping of the TiO₂can make it possible to improve the photocatalytic behaviour, ifnecessary.

[0116] It is also confirmed, from the comparison of Examples 2 and 3,that the nature of the sublayer influences the crystallization form and,in fact, the photocatalytic activity of the coating.

1-24. (Canceled).
 25. A process for a producing a coated float-glasssubstrate, comprising: chemical vapor depositing at least one titaniumprecursor on at least part of at least one face of a float-glasssubstrate produced in a float-bath chamber, to produce a photocatalyticcoating containing at least partially crystalline titanium oxide. 26.The process of claim 25, wherein the coating containing the at leastpartially crystalline titanium oxide has a degree of porosity of 65 to99%.
 27. The process of claim 25, wherein the coating containing the atleast partially crystalline titanium oxide has a degree of porosity of70 to 99%.
 28. The process of claim 25, wherein the coating containingthe at least partially crystalline titanium oxide has a degree ofporosity of 70 to 90%.
 29. The process of claim 25, wherein thecrystalline titanium oxide is in the form of crystallites with anaverage size of between 0.5 and 60 nm.
 30. The process of claim 25,wherein the crystalline titanium oxide is in the form of crystalliteswith an average size of between 1 and 50 nm.
 31. The process of claim25, wherein the crystalline titanium oxide is in the form ofcrystallites with an average size of between 10 and 40 nm.
 32. Theprocess of claim 25, wherein the crystalline titanium oxide is in theform of crystallites with an average size of between 20 and 30 nm. 33.The process of claim 25, wherein the thickness of the coating containingthe at least partially crystalline titanium oxide is between 5 nm and100 nm.
 34. The process of claim 25, wherein the thickness of thecoating containing the at least partially crystalline titanium oxide is10 nm to 25 nm.
 35. The process of claim 25, wherein the thickness ofthe coating containing the at least partially crystalline titanium oxideis between 5 nm and 20 nm.
 36. The process of claim 25, wherein thecrystalline titanium oxide is in the form of crystallites and thethickness of the coating containing the at least partially crystallinetitanium oxide is at least two times greater than the mean diameter ofthe crystallites.
 37. The process of claim 25, wherein the crystallinetitanium oxide is in the anatase form, in the rutile form, or in theform of a mixture of anatase and rutile.
 38. The process of claim 25,wherein the titanium oxide is crystalline with a degree ofcrystallization of at least 25%.
 39. The process of claim 25, whereinthe titanium oxide is crystalline with a degree of crystallization ofbetween 30 and 25%.
 40. The process of claim 25, wherein the surface ofthe coating containing the at least partially crystalline titanium oxidehas a contact angle with water of less than 5° after exposure to lightradiation.
 41. The process of claim 25, wherein the coating containingthe at least partially crystalline titanium oxide of the coating has acontact angle with water of less than 1° after exposure to lightradiation.
 42. The process of claim 25, wherein the RMS roughness of thecoating containing the at least partially crystalline titanium oxide isbetween 2 and 20 nm.
 43. The process of claim 25, wherein the RMSroughness of the coating containing the at least partially crystallinetitanium oxide is between 5 and 20 nm.
 44. The process of claim 25,wherein the chemical vapor deposition is conducted at a temperature of400 to 600° C.
 45. The process of claim 25, wherein the chemical vapordeposition is conducted at a temperature of 400 to 600° C.
 46. Theprocess of claim 25, wherein the titanium precursor is a titaniumhalide.
 47. The process of claim 25, wherein the titanium precursor isan organometallic titanium compound.
 48. The process of claim 25,wherein the titanium precursor is a titanium alcoholate.
 49. The processof claim 25, wherein the titanium precursor is TiCl₄.
 50. The process ofclaim 25, wherein the titanium precursor is selected from the groupconsisting of Ti(OiPr)₄, titanium diisopropoxide diacetylacetonate,titanium tetraoctyleneglycolate, and titanium acetylacetonate.
 51. Theprocess of claim 25, wherein the coating containing the at leastpartially crystalline titanium oxide also contains at least one additivecapable of accentuating the photocatalytic activity of the titaniumoxide.
 52. The process of claim 25, further comprising incorporatingmetal particles or particles based on such a metal into the coatingcontaining the at least partially crystalline titanium oxide, whereinthe metal is selected from the group consisting of cadmium, tin,tungsten, zinc, cerium, and zirconium.
 53. The process of claim 25,further comprising inserting into the crystal lattice of the titaniumoxide at least one the metal is selected from the group consisting ofniobium, tantalum, iron, bismuth, cobalt, nickel, copper, ruthenium,cerium, and molybdenum.
 54. The process of claim 25, further comprisingcovering at least part of the coating containing the at least partiallycrystalline titanium oxide with a layer of metal oxides or salts,wherein the metal is selected from the group consisting of iron, copper,ruthenium, cerium, molybdenum, vanadium, and bismuth.
 55. The process ofclaim 25, wherein the coating containing the at least partiallycrystalline titanium oxide also contains an amorphous or partiallycrystalline oxide or mixture of oxides of the silicon oxide, tin oxide,zirconium oxide, or aluminum oxide type.
 56. The process of claim 25,further comprising coating at least a portion of the coating containingthe at least partially crystalline titanium oxide with a noble metal.57. The process of claim 56, wherein the noble metal is selected fromthe group consisting of platinum, rhodium, silver, and palladium. 58.The process of claim 25, wherein the substrate is coated with at leastone thin layer, wherein the thin layer has an anti-static function, athermal function or an optical function, or forms a barrier to themigration of alkali metals; and the coating containing the at leastpartially crystalline titanium oxide is coated on the thin layer. 59.The process of claim 58, wherein the thin layer has an anti-staticfunction.
 60. The process of claim 59, wherein the thin layer is basedon a conductive material of the metal type or of the doped metal oxidetype.
 61. The process of claim 60, wherein the thin layer is based onITO, SnO₂:F, ZnO:F, ZnO:Al, ZnO:Sn or a metal oxide which isstoichiometrically deficient in oxygen.
 62. The process of claim 61,wherein the metal oxide which is stoichiometrically deficient in oxygenis SnO_(2-x) or ZnO_(2-x), wherein x<2.
 63. The process of claim 58,wherein the thin layer has a thermal function.
 64. The process of claim63, wherein the thin layer is based on a conductive material of themetal type or of the doped metal oxide type.
 65. The process of claim64, wherein the thin layer is based on ITO, SnO₂:F, ZnO:F, ZnO:Al,ZnO:Sn or a metal oxide which is stoichiometrically deficient in oxygen.66. The process of claim 65, wherein the metal oxide which isstoichiometrically deficient in oxygen is SnO_(2-x) or ZnO_(2-x),wherein x<2.
 67. The process of claim 58, wherein the thin layer has anoptical function.
 68. The process of claim 67, wherein the thin layer isbased on a conductive material of the metal type or of the doped metaloxide type.
 69. The process of claim 68, wherein the thin layer is basedon ITO, SnO₂:F, ZnO:F, ZnO:Al, ZnO:Sn or a metal oxide which isstoichiometrically deficient in oxygen.
 70. The process of claim 69,wherein the metal oxide which is stoichiometrically deficient in oxygenis SnO_(2-x) or ZnO_(2-x), wherein x<2.
 71. The process of claim 67,wherein the thin layer is based on an oxide or on a mixture of oxideswith a refractive index which is intermediate between that of thecoating containing the at least partially crystalline titanium oxide andthat of the substrate.
 72. The process of claim 71, wherein the thinlayer is composed of Al₂O₃, SnO₂, In₂O₃, silicon oxycarbide, or siliconoxynitride.
 73. The process of claim 58, wherein the thin layer forms abarrier to the migration of alkali metals.
 74. The process of claim 73,wherein the thin layer is based on silicon oxide, silicon nitride,silicon oxynitride, silicon oxycarbide, Al₂O₃:F, or aluminum nitride.75. The process of claim 25, wherein the coating containing the at leastpartially crystalline titanium oxide is the final layer of a stack ofanti-glare layers.
 76. The process of claim 25, wherein the coatingcontaining the at least partially crystalline titanium oxide isdeposited in at least two successive stages.
 77. The process of claim25, wherein the coating containing the at least partially crystallinetitanium oxide is subjected, after deposition, to at least one heattreatment of the annealing type.
 78. The process of claim 25, whereinthe deposition is conducted at the outlet of the float-glass chamber inwhich the float-glass substrate is produced.